DESCRIPTION Cholesterol (Ch), the most prominent sterol of mammalian cells, is located predominantly in the plasma membrane, where it comprises 40-45 mol percent of the total lipid. Like other unsaturated lipids, Ch can be oxidized under conditions of cytotoxic oxidative stress. Among the oxidation products, cholesterol hydroperoxides (ChOOHs) are highly important because they can undergo iron-catalyzed 1-electron reduction, thereby triggering chain peroxidation reactions which expand the boundaries of membrane oxidative damage. Alternatively, ChOOHs may undergo glutathione-dependent 2-electron reductive detoxification if a selenoperoxidase (SePX) is encountered. Superimposed on these alternate fates (which are under study in the parent project) is the possibility that ChOOHs can move (or be transferred) from one membrane to another, either within or between cells. Little is known about this prospect. In this proposal to investigate ChOOH transfer, two hypotheses will be tested: (i) ChOOHs, being more polar than Ch, will translocate relatively rapidly from donor to acceptor membranes, and this can be enhanced by a sterol carrier protein; (ii) ChOOH transfer can be hazardous to an acceptor if its antioxidant capabilities are overwhelmed. The specific aims of the project are to examine: (i) spontaneous intermembrane transfer of ChOOHs (ii) sterol carrier protein-mediated intermembrane transfer of ChOOHs, and (iii) spontaneous vs. protein-facilitated transfer to mammalian cells and its cytotoxic consequences. The studies will involve, liposomal membranes, erythrocyte membranes, aortic endothelial cells, selenium and iron manipulation, and two unique analytical techniques developed during past interactions between the Principal Investigator and Co-investigator: high performance liquid chromatography with mercury cathode electrochemical detection, and high performance thin layer chromatography with radioimaging detection. In addition to strengthening collaborative ties between the host and foreign laboratories, these studies will provide insights into previously unrecognized ways by which cells might be exposed to the prooxidant/cytotoxic effects of ChOOHs. The work is biomedically significant because disorders such as atherogenesis and neurodegeneration are associated with lipid peroxidation, and ChOOH transfer may promote this process.